Electrical measuring instrument



sept, 30g-1930.

J. H. MILLER ELECTRICAL IEASURING INSTRUIENT Filed March 19, 192B '3 Sheets-Sheet 1 NNN , NSN

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Patented Sept.v 30, `1930 UNi'i" JOHN IrvMILLi'ia'or OAK PARK, ILLINOIS, AssIeNon ro JEWEILL ELECTRICAL `INsrnrr MENT CO., OF CHICAGO, IILIINOIS, A CORPORATION OF ILLINOIS nLEornIoALivIEAsuniNe INSTRUMENT Application iiledMarch 19, 1928. Serial No. 2G2,79

provide a plurality of separate scales of dift iercnt calibration and divisions upon ,the

dial. Theuse of `shunts or resistances involves additional equipment, ,more complicated electrical Wiring outside the instrument, and mental calculation to arrive at the correct result, thereby increasing the costof the instrument and equipmentand increasing the possibility of'error.- Itis also necessary to calibrate the instrument for each shunt, in

order to insure'accurate results.l The use of a plurality of scales of dierent division and calibration is confusing, and also expensive, increasing the cost of manufacture and the time consumedin maintaining accuracy by calibration or otherwise.V

One of the objects ot the present invention is the provision of a multi-range electrical measuring instrument which does notV require theuse ot auxiliary shunts or resistances and which is adapted to indicate accurately upon a` single scale having a pluralityof sets of numerals. c

Another object of the invention isthe provision of a novel casing structure for electrical measuring instruments, and a novel internal structure `which is easier to manufacture and assemble, more economical," more durable and more thoroughly insulated than the instruments of the prior art. t

Anotherobject of the invention is the pro'- vision of an insulating casing for electrical instruments Which is molded of a'phenolic condensation product such as balrelite,` and having a cover of the same material adapted desirable factors.' i

Another object oil the'invention is the provision of a novelactuating coilunit torelec- Y trical measuring instruments of the movable vane type, or other types, the separate Wires or coils of which are so located as to produce substantially equal magnetic eiiect uponmagnetic vanes, and which may therefore be'emf ployed for multi-range operation With a single division scale.

Anotherobj ect of the invention istlie profl vision of a novel indicating unitot the movaf` blevane type, Which may bemoreaccurately formed and insulated by constructing itssupporting member of molded bakelitefor thef` o like, thereby secui'inga more accurate operaliti tion and more effective damping,\and reducv ing the costof manufacture.

' Anotherobject of the invention'is the provision ot a novel instrument assembly including a supporting trama'which may also eii'ect magnetic shielding oftheinstrument against `terrestrial magnetism or `that pro-` i duced by adjacent electrical machinery.`

Other objectsand advantages of the invention Will appear more fully from the followingY description and from theaccompa-nying drawings, 1n which` similar characters of reference indicate similar parts throughout` y the several views. 7

Figure 3 is a topplan view of the coil unit Y and cover partially broken away to showthe interior ofthe damping chamber;

Figure 4i is an elevational view of the.

unitsshown in Figure 3, partially fbroken away to show the interior structure of the supporting posts;

Figure 5 is a medial cross-sectional view of the coil unit and indicating unit in assembled relation, taken on the line 5&5 of Figure 3;

Figure 6 is a plan cross-sectional viewr lite. The coil unit is formed with abase 11,

for convenience substantially rectangular in form, having an upwardly extending cylindrical member 12, terminating in an outwardlyA extending annular flange 13, forming a spool for the reception of the Ywindings 14.

Thefbase 11 preferably consists of av flat Vportion 15 of substantially rectangular shape, having downwardly extendingY walls 16, Y17, 18 and 19, at'each side, forming a hollow chamber 2O within which electrical connections may be made. In order toisolate the electrical connections from the mechanism of the indicating unit, the cylindrical wall 12 is extended downward as at '21, forming an accurately machined bore 22` within which the indicating unit fits.

The Hat portion 15 of the base 11 is slightly extended at one side to provide room for the reception of a plurality of terminals 23,

` 24, 25 and 26, which may consist of bolts 27 passing rthrough apertures 28 in the base 11 and secured thereon by'nuts 29. The bolts are provided with cap nuts 30 forsecuring electrical connectorsl, 32, 33 and 84 upon conductors, which lead to the external-ter-V minals on the instrument casing, further to be described, and the headsf35 of the bolts 27 are employed for connection to theV ends ofthe windings 14 by means of soldering or other convenient electrical connecting means. f

' I shall now describe t-he structure of the windings 14 which enable me to effect multirange operation upon a single dial, having a plurality of sets kof numerals. I prefer to wind the spool 12 with a cable composed of a plurality of conductors arranged in such manner that the'average position of each conductor is such that each separate coil produces substantially the same electro-magnetic effect within the bore 22 of the spool.

Referring to Figure 7, I have here illustrated a preferred form of cable, and for a three range instrument the cable may consist of nineteen conductors. The cable may be formed by making the central conductor 36 of insulated copper wire, which may be cotton coveredand impregnated with insulating cement, in order to assist in holding the conductors in proper position. About the central conductor 36 I place six other conductors 37, 38, 39, 40, 41 and 42. All of these conductors are twisted together in the saine direction, so that each conductor appears upon the same side of the cable a plurality of different times throughout the length of the cable, with the exception of the central conductor'36, which, of course, is located at the axis of the cable. Vithin the crevices existing between the conductors 37 to 42, I place six additional conductors 43, 44, 45, 4G, 47 and 48,y and Within the crevicesrformed bythe latter six conductors, I place six more conductors, 49, 50, 51, 52, 53

and 54. All of the foregoing conductors are Y twisted in the same direction, as previously stated, and by themethod descirbed, a substantially round cable may be formed which will be held together by the insulating cement, thereby facilitating the winding operation.

Thev cable 14 is weund upon the spool 12 in the usual manner, the beginning end of the cable being' passed through an aperture 55 inthe base 15 adjacent the cylindrical portion 12 of the spool. The cable is then wound inthe regular manner with a plurality of turns side by side tothe top of 'the spool, thence with a plurality of other regular turns downward tothe bottom of the spool, thence in a similar manner to the top in the present instance, and the opposite end of the cable may be passed through an aperture 56 into the chamber 2O ofthe base 11. 5 It will be obvious that any number of turns may be employed and any number of layers of winding, and itis possible by the foregoing method -to wind suficient cable upon the spool to secure the necessary amount of flux to actuate the instrument.

Referring to Fig. 9, I have here illustrated a wiring diagram 'showing the connections of the various conductors at the ends of the cable. Although the f various conductors are diagrammatically illustrated in F ig. 9, some being side by side and some being end to end, it will be understood by those skilled in the artthat the physical position of these conductors upon the spool is that they are all side by side, forming a part of the cable, and each conductor has a plurality of turns about the spoolV represented diagrainmatically in Fig. 9 byv a single loop. f

Referring to the wiring diagram, 57 indicates a common terminal marked i which lUU is used as one terminal ineach of the multirange operations. The numeral 58indicates the other terminal for the -ampere scale` marked 20A, the numeral 59 indicates the other terminal for the -ampere scale, marked 2A Y Y v In order to provide coils foractuation of ,the instrument on the (20-ampere range, I

select seven of the conduct-ors of thecable 14 and connect them in parallel between the terminals 57 and 58. 1rWhile some of the advantages of my invention may be realized by 1 selecting` any of the conductors of the cable, I prefer toselect these conductors from the of operation, I use the first mentionedseven conductors fin paralleli and connect thereto two sets of three conductors each in series, each set being in series withthe irst seven parallel conductors, and each set of three being in parallel with the-other. For this purpose I1 prefer to select the following conductors `from symmetrical points, inside and outside of the cable, and the second `set of siX conductors may consist of the conductors 42 and 39,` each having one end connected to the terminal 58; the conductors 43 and 46 from the exterior of the cable eachhaving an end oined with the opposite ends of the con- "ductors 42 and 39 as at the point 61; and theconductors `51 and 54 each having one end joined to the opposite ends of the conductorsV 43 and 46 as at 63, the opposite ends of the conductors 51 and 54 being connected to the terminal e 59 marked 5A.

For the third 2-ampere range of operation I employ theforegoing` connections together with the remaining six of the conductors of the cable connected in series with each other `and in series with the foregoing system of conductors. Thus one end of the vconductor connectedto the terminal 59 and the opposite end of the conductor 38 connected to one end of the conductor 41. The opposite end of the conductor 41 is connected to one end of the conductor 48; the opposite end-of the con# duct-or 48 is connected to one end of the conductor the opposite end of the conductor 45 is connected to one end of the conductor 53; the opposite end of the conductor 53 is connected to one end of the conductor. and the opposite end of the conductor'O is connected to the terminal 60 marked 2r.

It shouldbe noted'that in every case the-se the inside of the spool. rare the righthand ends of the'V conductors i 36, 37, 40, 44, 47, 49 and 52 and thev two conductors connected to this terminal are the" connections are so made that the current runs in the same direction through the coils of the` cable; otherwise the ampere turns of one coil would counteract the eft'ect of another.

Referring to Fig. 8, I have hereshown the actual electrical connections made withinthe base of the spool of the coil unit and referring to the terminal 57, it will be noted that seven conductors from one end of the cable are brought out and soldered to the head of theterminal 57. These are the left ends of the conductors 36, 37, 40, 44, 47,149 and 52.

Referring to the terminal 58,-it will be noted that there'are attached to this terminal seven conducto-rs coming from the outside of the spool and two conductors coming from left-hand ends of the conductorsi42'and 39.

noted that three conductors are 'secured to The seven conductors this terminal, two coming from the insidefof the coil being the right-hand endsof the con` ductors 51 and 54, and one coming from the outside of the coil, being the vleft-hand end of the conductor38. i

The intermediate connections at the points 61 and 630i the diagram in Fig. 9 are shown f in Fig. `8`und'er the same numerals, in each case four conductors being connected together. At the point 61 two conductors 39 and 42 coming from the outside of the coilare connected to two more conductors 43 and 46 coming from the Y inside of the coil. These are the right-hand ends of the conductors 39 and 42 connected to the leftfhand end of the conductors 43 and 46 in Fig. 9.

In a similar manner, the right-hand `end 50 are made by taking the right-hand ends of' conductor 38 fromthe outside of the spool and connecting to the leftshand end of con- 38 from the interior ofthe cable may. be

ductor 41; the right-handfend of the conductor 41 from the outside of the spool and connecting to the left-hand `end of the conductor 48 from the inside of the spool; the right-hand end of the conductor 48 from the outside of the spool and connecting to the leftha`nd end of theconductor 45.from `the inside of the spool; the right-hand end of the conductor 53 from the outside of the Vspool and connectino' to the left-handend of the conductor 50 from the inside of the spool, respectively.

As previously stated, the right-handend of the conductor 5() connected to the terminal In the foregoing explanation, the righthand endv of anycoil as shown in Fig. 9 is taken as the end of the'coil emerging from the opening/256k at-'the outside of thespool and the left-hand end of any coil as shown in Fig. 9 isvtaken as the end of the coil in Fig. 8 emcrgingfrom the opening 55 at the insideV of the spool. The connections described are preferably made by soldering the wires to the terminal and by soldering the respective wires together at their ends as described and covering the soldered joints by a short piece of tubular insulation known as macaroni.

I shall now illustrate how the foregoing lconnections Vproduce a magnetomotivev `force each of the conductors 86, 37, lit), 4%,417 9A and 52, since these conductors are connected in parallel. The total ampere-turns will then be: c y

/7 amp. X 7 wires X 12 turns per wire 240 amp-turns.

Y Vhen the instrument is employed upon the 5-ampere range andiive ainperes are passing through the iiistrument, the amount of cur` rent in the first seven conductors will 5/7 amperes per conductor,'since these are connected in parallel and the current will be equally divided among them.

' Since the next conductors are connected in two parallel rows ofthree each,`t'he current of five amper-es will be divided equally between these two roi and two and onehalf amperes will pass through each conduc' tor.

A The total number of ampere-turns for this range of operation may then be vcalculzd'cd as follows:

For the first seven conductors 5/7 amp. X 7 wires X 12 turns per wire :G6 amp.tums

For the Second set of six conductors 2/ amp. X 6 wires X 12 turns per wire :180 amp-turns I amp.-turns F or the third range of operation of two' amperes, ve may likewise calculate the number of ampere turns at full scale indication of two amperes as follows:

For the first set of sevenconductors in par-` allel, the two amperes will be divided equally among these coils, giving 2,/7 of an am )ere per coil; for the second set of six conductors in two rows of three coils each, the two amperes will be divided between ythe two branches equally, giving one ampere per coil; and for the last six conductors in series, there will be two amperes flowing through each coil.

The total number of ampere-turns is calculated as follows:

For therst seven conductors 2/7 amp. X 7 Wires X k12 turns per wire :24 amp .-turns For the Second set of six conductors 1 amp. X Grwires X412 turns per wire =72 amp.-turns For thevlast set of six conductors 2 amp. X 6 wires X l2turns per wire :144 amp-turns Iotal r v ;240 amp-turns It will thus be observed that at the current value corresponding to the full scale of each range of operation, the number of ampereturns of magneto-motive force is the same for each rangeY and the repel-ling force generated between theinoving vane and the fixed vane will be equal under these circumstances for each range of operation.

t will be evident to those skilled in the art that with the foregoing arrangement of coils and electrical conne'ctions,'they instrument will likewise be adapted to indicatev at the same point for each of the three rai'xges: for fractional values of the full range current, and I am thus enabled to use a single scale for a multiple range instrument without the assistance of auxiliary shunts or series resistances. The arrangement of the respective coils in a cable so that the average position of each coilY is practically the same, producing substantially the same magnetic effect upon the varies, and the selection of the conductors from symmetrical points within the cable have been found to .produce a high degreev of accuracy with the single scale employed. Y

Referring now to Fig. 1, l shall describe the electrical connections between the terminals 57, 58, 59 and 60 and electrical connectors 65, 66, 67 and 68 located upon the exterior of the casing 69.

The connectors to 68 inclusive may be of any standard construction, and in the present embodiment may consist of an enlarged cylindrical exterior' metal body 70 having a transverse aperture 7l adapted te receive a conductor and having` an axial bore 7 thread* ed to receive a clamping screw bolt 73. T he opposite end of the body 70 is likewise provided with an axial bore threaded to receive a screw bolt 74: passing through a flat electrical connector 75, and through the wall 76 of the casing to clamp said connector and the wall of the casing between the head of the screw and body 70 of the connector.

As the casing 69 is preferably constructed of insulating material, no insulating washers are located upon the'connectors which are effectively insulated from each other by the casing itself.

The terminal 57 upon the coil unit is conadjacent the'tcrminal.- This isI the common terminal which is employed orvuse of any of the three ranges `of operation.` I

`In a similar manner, `the terminal 58 1s connected by means `ot aV connector 32, conductor 78 and connector 7 5 to the terminal 66 desig- Y nated QOrrlto indicate the terminal for the 20 ampere range of operation.

The terminal 59 upon the coilunit is likewise connected by meansof a connector 33, conductor and connector 81to the terminal 67 carried on the exterior of the casingand designated 5A to indicatethe second terminal for the 5-ampere range of operation.

The terminal 60 upon the coil unit is con-` nected by'means ot' a connector 34, a conductor 82 and a'connector 83 to the terminal 68 carried on the exterior of the casing, ,and designated 2A to indicate the second terminal for the Q-ampere range of operation.

The connectors 31 to 34 and 75, 79, 81 and 82 comprise lat'p'ieces of metal having apertures to receive thejscrew bolts of the terminalsv and having a' projecting flange to which/the conductors 77, 78, 80 and 82 may be soldered. i.

` 1 shall now describe the Vstructure of theV indicating unit of mymeasuring instrument, and by the term indicating unit`1 designate that portion (of the structure, supporting and including the movable mechanism actuated by the coil unit. i

,Referring to `Fig. 5, 84 indicates in its entirety my indicating `unit which comprises a bodymember 85 preferably constructed by molding the same of insulating material such as bakelite. Thelupper portion of the body 85 is substantially semi-circular in vcross-section asshown in Fig. 3 and is formed with the fan-shaped damping chamber86. The damping chamber is thus provided with two concentric circular walls` 87 and 88, a flat bottom 89 and a pair of radial wallsv90 `'and 91. rllhe top of the damping chamber 86 is open, being closed bya coverplate 92 of sheet metal andl of 'a size adapted to overlie e-ach of the-walls 90,91, 87 and 88. K l

' The cover plate 92 is preferablysetin a groove 93 at the top of said walls, flush with the upper surface of the body 84 and the cover plate may be secured in place `by a plurality of screw bolts 94 threaded through a shield (further to be described), and the cove-r plate into the bakelite body 84.

Y The body 84V isprovidedat [the side opposite the-damping'chamber 86 with a groove 95 extending parallel, to the walls 87 and 88 and adapted to house a spindle 96. The body 84 is also provided withwanvintegral downwardly projecting lug 97 having one side 98 formed like a portion of acylinder andthe yopposite side 99 forming an extension of the groove 95. The lower end of the eX- tensionv 97 extends at substantially right,

angles as at 98 and is provided with a threaded member 99A molded therein, and adapted f to'receive a threaded screw .bolt 100 having j a jewel101 and a kerf`102-` The threaded member 99 is of substantially cylindrical eX- terior shape and projects from the transverse portion 98 by an amount equal tothe thick Vness of the wall 103 of the insulating cylinder 104. Y

The insulating cylinder 104 comprises an insulating member preferably constructed of bakeliteand adapted to lit accurately within the cylindrical bore 22 of the coil unit 11.

The insulating cylinder 104 is provided with a fiat bottom 103 having a centrally disposed bore 105 adapted toV lit about the threaded member` 99.

, The interior of the insulating cylinder 104 islikewise cylindrical in form and theupper end of the cylinder is adapted to litaboutan annular shoulder 106 formed upon the body l 84 about the groove 95. While the-,annular shoulder 106 does not forma complete circle, it extends beyond thev range of a semi-circle on each side, thereby providing` suticient cylindrical surface upon the annular shoulder 106 to definitely fxltheposition of the upper end of the insulating cylinder 104.

The annular shoulder v106 is provided at any point 107 with. a projecting lug which is adapted to extend into a complementary groove 108 on the insulating cylinder 104.V It will thus be observed 'that the lug 107 con-` stitutes a stop member which prevents relative rotation between the insulating cylinder and the body 84 of the indicating unit.

The insulating cylinder is provided with a liXed vane 109 comprising a relatively thin piece of sheet metal of magnetic properties bent to cylindrical form and molded within the insulating cylinder 104 Hush with its inner surface. The fixed vane maybe provided with a pair of air holes 110 and it will be observed that the location of the stop lug `107 also determines the proper position of the lixed magnetic vane relative to the other parts of the mechanism.

The indicating unit body 84 is provided with. a. pair ofscrcw bolts 111 and 112 molded within the insulating `body and projecting from its upper surface on either side of the groove 95. The screw oolts 111 and`112 are accurately located relative to the threaded through apertures -in a bridge comprising a short strip of sheet metal. rlhe bridge 115 is provided with a centrally located threaded bore 116 adapted to receive a screw bolt 117 having Aa kerf 11S at one end. and a liewel 119 at the opposite end. Y Y

- The screw bolts 114 and 113 which secure the bridge tothe indicating unit are-also employed for securing'a pair of stop members 120 and 121, each comprising a short length of flat wire having one loopsecured beneath one of the screw bolts 113- or 114 and extending forward on either side above the damping chamber 86 to provide a stap for the pointer 122.` v c At their forward ends the stop members 120 and 121 are bent up at 'substantially right angles and this bent-up portion is covered by a short tube of lava 123, the tubes being secured in place by bending over the ends of the wire projecting fromthe tube. I prefer to use stop members of lava for the reason that I have found that there is no adhesion, electrical or otherwise, betweenthe pointer and the stop member of lava which will prevent the actuation of th-e needle at very small current values, such as would be the case were glass or other insulating tubes employed.

The pointer 122 may consistof a light aluminum member formed of sheet metal havinga small central plate 124 with an aperture adapted to receive the spindle V96 and a plurality of threaded arms 125 adapted to receive nuts 126 for the purpose of balancing the pointer 122. kThe pointer is preferably ormed with a fork 127 extending` from the plate 124 ending ina single arm 128 which istlattened at 129 in a plane perpendicular to the dial 130.'V f

VThe spindle 96 comprises a light aluminum rod which is formed with an integral iange 131 adjacent its upper end, a reduced threaded portion extending upward fromV said llange. The damping vane 132 comprises a thin aluminum plate provided with transverse corrugations 133 for increasingr` its strength and withllanges 134 and 135 about its edge at substantially right angles for the same purpose. Y

The size of the damping vane 132 is such that it iits accurately within the damping chamber 86 and it is adapted to be supported upon the spindle 96 extending` from the curved surface 87 to its concentric surface '38 and swinging in an arc within the damping chamber. 1

The dampingvane 132 may be supported upon the spindle by a plate of sheet metal 134 Yhaving a' projecting arm 135 extending into the boxlike damping vane belowv the upper flange 135. The damping vane may be secured to the arm 136 by It should also be noted that the short bending down aV .portion 137 of the flange 135 about the arm Lvvaves curved wall 88 of the body 84 is slightly shorter than the other walls of the damping chamber providing an aperture 138 between the wall 8S and the cover plate 92 through which the arm 136 may extend into the dam p'- ing chamber.

Above the damping vane plate 134 the spindle may be provided with a spacing member 139 after which the pointer 122 may bei placed upon the spindle and secured by a nut'140. Each end of the spindle is provided with a hardened steel point 141 and 142 adapted to be journaled in the jewels 119 'and 101 respectively,to rotatably support the spindle with a minimum of friction. f

At the lower end of the spindle adjacent the insulating cylinder 104 and the tixed magnetic vane 109, the spindle carries a second vane 143 of magnetic material which will be hereafter called the movable vane, being supported for rotation by means of the spindle 96.

Y The movable vane 143 vcomprises a relatively thin piece or" sheet metal of substantially the same size as the fixed vane 109 and bent concentrically withthe interior of the insulating cylinder 104 and with the surface of the ixed vane-109 from which it is spaced a very small distance.

Y The movable vane 143 may be supported by a pair of sheet metal arms 144 and 145. each comprising aA thin plate of sheet metal of substantially the shape shownin Fig. 6, having an aperture 146 adapted to receive a sleeve 147 and having an outerV curved edge 148 with a plurality of projecting lugs 149. The movable vane 143 may be affixed to the arms 144 and 145 by passing the lugs 149 through apertures 150 in the movable vane and riveting the vane upon the arms by means ot' said lugs. v

The arms 144 and 145 may be secured to the spindle 96 by means of asleeve 147 adapted to lit closely about the spindle 96 and secured thereto by a pin 151 riveted through said sleeve and spindle.

The sleeve 147 is vprovided with an annular shoulder 152 at each end and a reduced cylindrical portion 153 at each end adapted to be received in each of the apertures 146 of' the arms 144 and 145. The arms 144 and 145 may then be secured to the sleeve by riveting or peening overl the ends of the sleeve as at 154.

The spindle 96 is also provided with resilient means for `biasing thepointer to zero position and for resisting the forces of repulsion generated by the electromagnetic flux 01:' the coil unit. This resilient means may consistof a coil spring 155 consisting spindle by providing theend of the spring with an aperture. adapted to receive the threaded end of the spindle and Lto be clamped in place by thev nut 1&0.

The outer end of the spring,` is preterably secured to a downwardly turned flange 157 ot azero adjustment lever 158 by solder ing or other Yconvenient ,fastening means. The Zero 'adjustment lever 158 comprises a relatively'thinplate of sheet metal having an aperture 159 adapted to receive the reduced end 160 of the nut 161 and also having a downwardly vturned flange 157 adapted to be secured to the spiral spring 155.

The nut 161 consists of an ordinary nut having `a reduced cylindrical portion 169 adapted to rotatably support the zero adjustment lever 158 and also to support a crimped` spring washer 161A` interposed between the zero adjustment lever 158 and the bridge 115.' `The nut 161 maybe threaded upon the screw bolt 117 into engagement with the bridge 115also serving as a lock nut for the jeweled screw bolt 117. f

At the opposite endet` the spindle the jeweled screw bolt 100 is also provided with a lock nut 100A serving to lock the screw bolt in place'and to retainfthe insulating cylinder 104 upon the indicating` unit.`

At the opposite end of the flange 157 the zeroadjustment lever is provided with an elongated slot 162 which is adapted to receive a pin 168 eccentrically carried by a molded balrelite member 16a rotatably supported upon the cover165.

The cover 165 is preferably provided with a bore 166 adapted to receive the head of an adjustment screw 167 flush with the upper surface, and with a counter-.bore 168 for receiving the stem of the adjustment screw 167. The adjustment screw 167 is provided with a flattened or noncircular inner end 169,1ulapted te be received in a comple- 167 by a small screw bolt 171 passing through a central aperture inthe insulating' member and `tlneaded in the end of the adjustment screw 167. i L i Themolded insulating member 161 may be of substantially cylindrical shape, having a` metallic pin or -wire 168 secured therein by molding the same in place.'substantially parallel to the axis ot' the cylinder, but eccentrically disposed relative to said axis.

In order to retain the adjustment screw 167 in any adjusted position, I prefer to provide a liber washer 172 and a crimped spring washer 17 3 interposed between the insulating` member 164 and the lower surface or' the cover 165. When the cover is in proper. position, closing the instrument, the pin 168 projects into the slot 162 of the Zero adjustment lever.

It will thus be observed that by insertingr a screw driver or other instrument in the lrerf of the adjustment screw 167 and by rotating said screw, the pin 163 will be caused to movein an arcuate path, sliding in the slot 162 and rotating the z ero adjustment lever 158 in a similar direction.

The rotation of the Zero adjustment lever 158 will carry with itthe outer end ot the spring' 155 causing the inner end oic the `pring to rotate the spindle 96 and the pointer 122V until the point-er reaches the proper Zero position. Y

1 shall now describe the nevel insulating casing` in which my electrical measuringi`n-` strument is enclosed. The casing 69 may consist ofan enclosing member of any convenientshape, but preferably having' a flat bottoni 17a andtour side wallsl17 5, 176, 177 and 178 at substantially rightlangles tothe base 174:.` The corners 179 are preferably rounded to presenta finished appearance andto prevent the chipping off of pieces as might be the case wer sharp corners employed. i j Y I prefer to form the enclosing member 69 otmolded insulating material such as bakelite and 1 provide the wallsfe` the-cash with ribs 180 in each 'cornergetending from the bottom to a point adjacent Vthe open top 181. The corner ribs are preferably provided with nuts 182 molded therein at their upper ends and Vadapted to be used in conjunction with screw bolts 183 tor securing the cover 165 upon the casing 69. Similar ribs and nuts may also be provided asvat 184` at intermediate points on the inside et the walls 177 and 178.

In order to secure the dial 189 h l also'pro-V vide a pair ot similar ribs 185 havim` Cin'n Vlar threaded nlembers 186 for securing the upper end of the dial 180 by means of screw bolts 187 and the bottom 174 of the casing` is provided with a plurality of apertures 188 disposed to .register with apertures 189 inthe coil unit and apertrui'es 190 in the shield (further to be described) for securing` the coil unit and shield to the base by a pluality of screw bolts 191.

The apertures 188 are preferably providr-xd with enlarged counter-apei-tures 192 adapt ed to receive the non-circular*head 198 ot the nut 194- tlushwith the bottom of the casing'. Y j Y i' As previously described, the walls 177, and 178 are also provided with apertures `for se- Vcuringfthe electrical connectors 65, 66. G7 and 68 which form the exterior terminals of the instrument. I

In order to provide the casing with a handle, the walls 177 and 178 may each support a screw bolt 195 secured to the wall by a nut 196, said screw bolt having a pair of spaced heads 197 and 198 forming a groove lili) RUG 199 adapted to receive the slotted and apertured ends 200 of a leather strap 201.

The strap may also be provided with a reinforcing strap 202 secured vto its underside by stitching 203 in order to give the handle the required degree of stiffness.

The cover 165 comprises a closure of substantially the same shape as the casing 69, having a flat top 204 and 'depending walls 2057 206, 207 and 208. rlhe walls 205 to 208 are of relatively small depth, being provided only for the rpurpose of giving clearance for certain parts carried by the cover, such as the window 209and its securing screws 210.

The cover 165 is provided at its upper half with an aperture 211 formed with a beveled outer edge 212,` and an inner shoulder 213 adapted to support the window 209. The window 209 lies against the shoulderl 213 on the inside of the cov-er and is secured in place by a plurality of spring fingers 214 carried by screws 210 passing through spacing sleeves 215 and threaded into the cover 165. A layer of plastic cement is also interposed between the shoulder 213 and the glass 209 in order to secure a dust-tight joint.

In orderto insulate completely the instrument and'to increase the factor of safety for those using theinstrument, I prefer to form the cover 165 of molded insulating material such as bakelite in the same manner asthe casing 69, thecover being provided with a plurality of apertures for receiving screw Y bolts 183 to secure the cover to the casing 69.

In actual practice it is found, however, that it is practically impossible to mold an insulating casing of substantial size such as is required for an electrical measuring instrument of this type, and to mold a complementary insulating cover which will fit accurately upon each other without any warping, rocking or substantial cracks at various points between these members.

-In order to obviate this difliculty and to provide a. dust-tight casing, I interpose between the casing 69 and the cover 165, a skeleton frame 216 which may be also formed of molded insulating material, and which is preferably provided with a rounded outer edge 217 forming a rib. The skeleton frame 216 comprises afour-sided frame having an upwardly projecting flange 218 adapted to be slidably received within the walls of the cover and a downwardly projecting flange 219 adapted to be slidably received within the walls of the casing 69.

Just outside the lianges 218 and 219, the skeleton frame is provided with grooves 220 above and below, and adapted to receive resilientskets 221 which may consist of rubber bands of a size adapted to fill said groove and to project above the top and bottom of the bead 217. The skeleton frame is also provided with projecting lugs 222 at the corners and sides,the lugs having apertures 223 to receive the same screw bolts 183 which affix the cover 165 to the casing 69.

It will thus be observed that when the casing, skeleton frame and cover are assembled as shown in Fig. 2, the skeleton frame may be firmly clamped between t-he cover 165 and casing 69 and the resilient gaskets 221 will compensate for any unevenness of fit or warping` between the cover and casing.

`Furthermore, since it is inevitable that cracks must appear at some points between the juncture of the cover' and casing, I prefer to provide the skeleton frame having an exterior rib 217 which naturally provides cracks 224 or crevices 225 on either side of the rib, and the slight additional discrepancy of fit between the cover and casing is thus added to the cracks on either side of the skeleton frame rib which renders any unevenness of fit invisible to the eye.

In order that the coil unit, indicating unit, casing and dial, may be firmly and accurately assemblerhand in order that the electromagnetic mechanism may be shielded from outside magnetic effects, 1 prefer to provide my measuring instrumentwith a supporting frame 226 which also comprises an electromagnetic shield for the same. The shield 226 may consist of a strip of sheet metal of sufficient width to embrace the spool 12 and coils 14 and bent to the conformation shown in Fig. 4.

The shield 226 thus has a flat bottom 227 which is apertured to receive the same screw bolts 191 which fasten the coil unit to the casing and the shield has a pair of upwardly extending walls 228 of the same height as the combined coil unit and indicating unit as shown in F ig. 4, terminating in outwardly bent afi'iXing flanges 229.

The top of the shield is completed by a pair of similar plates 230 and 231 of sheet metal of paramagnetic material, having grooves 232 for the spindle 96, for the threaded members 112 and 234, and for the screw bolts 235 which secure the indicating unit to the coil unit.

Vhcn the plates 230 and 231 are laid across the securing flanges 229 on either side of the spindle which is above the body of the indicating unit 84, the grooves 232, 233 and 234 form circular apertures embracing the spindle and vbolts aforementioned, so that the shield plates 230 and 231 may be affixed after the coil unit and indicating unit have been assembled.

The shield plates are secured in place by screw bolts 236 passing through the outer edge of each plate into the securing flange 229 of the shell frame 226, and also by the screw bolts 94 passing through both the shield plate 231 and cover plate 92 of the damping chamber 86 into the body 84 of the indicating unit.

In order that both shield plates may be Aidentical for convenience of manufacture, all

of the shield plates 230 and 231 are also provided with apertures for the screw bolts 94 although not required on 'the shield plate 230.

Besides the shielding frame 226, theindieating unit and coil unit are also provided with means torsecuring the same together,

comprising a. pair 4oi metal posts 237 secured at one end to the indicating unit and atthe opposite'end tothe base of the coil unit 11. F or this purpose the base of the coil unit may be providedV with a pair of Abores 233, one at each side, each leading to a counter-bore 239 above and a counter-bore 240 below.

The counter-bore 239 is adapted to receive the end of the cylindrical Vpost 23?' which is seL cured in place by a screw bolt 241-having its head concealed in the counter-bore 240 nand .its opposite end threaded into a threaded bore 242 in the posts 237.

The posts 237 are of suiiicient length so that when the indicating unit has its cylindrical insulating member 104 in proper position in the` bore 22 and its body '34 resting flatly upon the upper `flange 13 ot the spool, the upper` ends ot the posts 23'? lie' against the lower edge of the body 84 'of the indicating unit at each side. The body 84 of the indicating unit may then be secured to the posts `237' and to the coil unit by a pair of screw bolts 243 passing through vthe body 34 and threadedinto the posts 23'?.

Thenon-circular heads 244 of the screw bolts 243 are embraced by the grooves 234 of the shell plates 230 and 231, but do not interfere therewith and the heads 244 are provided with threaded apertures 245 adapted to receive screw bolts 246, securing the lower end of the dial 130 to the coil unit and indicating unit.

The dial 130 comprises a flatplate of sheet metal such as brass or the like, having its upper surface covered with a layer of paper cemented or otherwise secured thereto. dial plate isvprovided with grooves 247 for the reception of the -ribs 222 atthe corners and sides of the casing, and as previously de` scribed, the dial is altiXed to the casing at the top by screws 187 and to the indicating unit at the bottom by screw bolts 243;

The dialv is provided with a single arcuate scale 248 having radial division 'marks 249 of the usualtype and proper calibration.

As my multiple range instrument is adapted to read upon `the same scale .divisions'iu each range, but one set ot' scale divisions is vrequired and a plurality of sets of numerals is employed. Thus the lower set of numerals 250 ranges from Zero to two amperes; above 4the scale the second set of numerals 251 ranges from Zero to twenty amperes, and above thisl set ot numerals is a third set 252 ranging from zero to live amperes. y y

Below the arcuate scale divisions, the dial is provided with the usual arcuate slot 253V continuous magnetic circuit. The

in the paper cover, exposing a mirrored surface upon the dial plate which serves the usual purpose of enabling the operator `to toavoid the errors in reading the instrument, which' are due to improper location of the eye. l

The assembly of the foregoing parts willV be obvious to those skilled in the artV and the` operation of the instrumentis as follows:

It will be evident that the operation is the same for any one range of operation, whether it be 2-ampere`, 5-ampere`or 20-amperevl desire it to be understood that theV foregoing vranges of operation are merely illustrative of one embodiment of my invention and'I do not wish'to be limited to the ranges set forth. lt should also be understood that the specific form olf the cable may be varied, while still realizing many advantagesof my` invention,l and my invention includes other equivalent arrangements of conductors and connections according to the same principle of operation. i

My electrical measuring instrument may be employed either as an ammeter or volt meter, depending upon the resistance of the coils employed and the methodof their connection.;

In the use of my instrument l'as an amiA and any other one of the terminals in an place his eye directly above the flat pointer electrical circuitwill permit the flow of cur-` rent in the circuitthrough the correspond# ing electrical conductors connected to said terminals. The current flowing through the corresponding coils willresult in the generation of linesof magnetic tluxpthe direction ot which Vwill be controlled by welllknown physicallaws and which will result inthe passage of flux in a certain direction through the bore 23 of the coil unit andv out-V ward about the coilto meet'each other in a The fixed magnetic vanef 109 and the movable magnetic vane 143 being included in said magnetic fcircuit andjpresenting a muchlesser reluctance to the passage of ioo magnetic ylines of lluX than .the air, the tend-v y ency of such lines of flux will `be toV pass through said magnetic vanes as far as. possible, polarizing said vanes, anda resultant force will be developed between the two magnetic vanes due to the proximity oflike magnetic poles at each` end of the vanes,

causing the vanes to repel each other.

The magnetic vane 109 being fixed and the magnetic vane 108 .being pivoted uponA the spindle 96, the latter will be repelled from the former and rotated with the spindle 96 away from the .iiXed vane, and the force tending to separate these vanes will be opposed by the spring 155. A

The scale 248 is accurately calibrated to `indicate the number of amperes :flowing in the `circuit in which the terminals of the T member, a

the quantities measured upon a single scalel With accuracy; Which is enclosed in an insulating casing and constructed of molded insulating parts in such mannerl that the instrument is better insulated and more safe for use than any of the instruments of the prior art; and Which is more economically manufactured and more accurate than the instruments Which employ shunts or series resistance for multiple range operation.

While YI have illustrated and described a specific embodiment of my invention, many modifications may be made Without departing from ythe spirit of the invention, and I do not `Wish to be limited to Ythe precise details of construction set forth, but desire to avail myself of all changes Within the scope of the appended claims. f Having thus described myv invention, What Ik claim is neW and desire to secure by Letters Patent of' the United States is:

Y 1. In an electrical measuring instrument, a coil unit comprising a supporting spool member, and a symmetrically twisted cable Wound upon said spool member to form a plurality of coils, having'tlieir component parts substantially uniformlyV distributed' parts vsubstantially uniformly distributed about said spool to'sproduce substantially equal magnetic effect Within said spool, one

set .of said coils being connected: in seriesl forone range of instrument indication, and

la. secondset of paralleled coils being connected in series With saidiirstset for a second range of instrument indication. n

3. In an electrical measuring instrument, a coil unit comprising a supporting spool -for one range of instrument indication, and

asecond set of paralleled coils beingconnected in series With said first setfor a second range of instrument indication, Yindicating means symmetrically formedv cable' actuated by said coils when energized and a scale for indicating on either range of operation.

4. In an electrical measuring instrument, a coil unit comprising a supporting spool member, a" symmetrically Aformed cable WoundV upon said spool member to form a plurality of coils, having their component parts substantially uniformly distributed about said spool to produce substantially equal magnetic eiiect Within said spool, one set of saidfcoils being connected in series for one rangeof instrument indication, and a second set of paralleled coils being connected in series With said first set for a second range of instrument indication, an instrument -terminal connected at one end of said first-mentioned set, a second terminal between said sets and a third terminal at the other end of said second set. f

. 5. In an electrical measuring instrument, aicoil unit comprising a supporting spool member, and a symmetrically formed cable Wound upon said' spool member to forni a plurality ofy coils, having their component parts substantially uniformly distributed about said spool to produce substantially equal magnetic effect Within said spool, one set of said coils being connected in series for one range of instrument indication, and a second set. of paralleled coils being connected in series With said first set for a second' range of instrument indication. the coils for each of said sets being selected from symmetrical points in said cable.

6. In an electrical measuring instrument, a coil unit comprising a supporting spool member, and a symmetrically formed cable `Wound upon said spool member to forni a plurality of coils, having their component parts Vsubstantially uniformly distributed about said spool to produce substantially equal magnetic effect Within said spool, one set of' said coils being connected in series for one range of instrument indication, a second set of paralleled coils being connected in series with said first set for a second range of instrument indication, and a third set of coils in parallel With each other and in series with said firstmentioned and second sets, for a third range of operation. l

r7.- In an electrical measuring instrument, a coil unit comprising a supporting spool member, and a symmetrically formed cable Wound upon said spool member to forni a plurality of coils, having their component parts substantially uniformly distributed about said spool to produce substantially equal magnetic eli'ect Within said spool, one set of saidcoils being connected in series for one range of instrument indication, a second set of paralleled coils being connected in series with said first set for a second range of instrument indication, and third set of coils in parallel Witli each other and in series `with said first-mentioned and second sets, for a third range of operation, the coils for each of said sets being selected from symmetrical points in said cable. i

8. In an electrical measuring instrument, a coil unit comprising a supporting spool member, a symmetrically formed cable wound upon said spool member to form a plurality of coils, having their component parts substantially uniformly distributed about said spool to produce substantially equal magnetic effectwithin said spool, one set of said coils being connected in series for one range of instrument indication, a second set of paralleled coils being connected in series with said rst set for a. second range of instrument indication, and a third set of coils in parallel with each other and in series Vwith said first-mentioned and second sets, fora third range of operation, a com-A i a coil unit comprising a supporting spool member, a symmetrically formed cable wound upon said spool memberto form a plurality of coils, having their component parts substantially uniformly distributed about said 'v spool to produce substantially equal magnetic effect within said spool, one set of said coils being connected in series for one range of instrument indication, a second set of paralleled coils being connected in series with said first set for a second range of instrument indication, and a third set of coils in parallel with each other and in series with said firstmentioned `and second sets, for a thirdrange of operation, indicating means actuated by said coils when energized and a scale for indicating on either range of operation.

10. In an electrical measuring instrument, a coil unit comprising a supporting spool member, and a symmetrically formed cable wound upon said spool member to form a plurality 'of coils, having their component parts substantially uniformly distributedV l a coil unit comprising a supporting spool member, and a symmetrically formed cable wound upon said spool member to form a plurality of coils, having their component parts substantially uniformly distributed about said spool to produce substantially equal magnetic effect within said spool, said cable comprisingV nineteen conductors ,l connected as follows; one coilend ,connected to a terminal, three coilends connected to a second terminal, nine coil ends connected to a third terminal,sevencoil ends connected to a fourth` terminal, five. sets oftwo coil ends each, connectedby twos, and two sets of four eachcoiinected by fours.

l2. In. anu electrical measuring instrument an indicating Vunit comprising a ybodyiiiember of molded insulating material-having a ,13.` In an electrical measuring instrument an indicating unit comprising -a body member of molded,insulating material having a@ plurality-.of threaded .members `molded therein, a bridge carriedlby a pair of said `threaded members, a jewel carried by said bridge,'a jewelcarriedv by another of lsaid threaded members, aspindlerotatably mounted inr said jewels,`-aniagnetic vane carried by said spindle, and a magneticjlvane carried by said body member. j i 14.V In an electrical? measuring instrument an indicating unit comprising a bodymeinber of molded insulating material having a plurality of threaded'members molded'therein, a bridge carried by a pair of said threaded members, a jewel carried by said bridge, a jewel carriedbyanother of saidltlireaded members, a spindle rotatably mounted in said jewels, a magnetic vane carriedby' `said spindle, a magnetic vane carried by said. body member,"said body memberhaving a damping chamber molded therein, and a damping vane carried ,by said spindle in said chamber.

l5. In an electrical"measuring instrument, the combination of a' molded insulating spool having a base and a bore therein, with a pair of posts carried by said b'ase, an indicating unit having a molded insulating body and a cylindrical portion fitting in said bore, a fixed vane carried by said body, a movable vane carried by said body, indicating means operatively connected to said movable vane, and means for securing said body to said posts.

16. In an electrical measuring instrument, the combination of a support with movable indicating means carried thereby, and a coil unit having a plurality of symmetrically located and twisted conductors permanently connected together and provided with leads for selective use of the coils for different ranges of measurement.

17. In an electrical measuring instrument, the combination of `a support with movable indicating means carried thereby, a coil unit having a plurality of symmetrically located and twisted conductors permanently consaid leads for use in connecting the connected together arid-provided with `leads forl selective use ofthe coils `for different ranges of measurement, and connectors carried by ductors in external circuits. v e

18. .In an electrical measuring instrument, the combination of a support with movable indicating means carried thereby, a coil unit having a plurality of symmetrically located and twisted conductors soldered together and provided with leads'for selective use'of the coils or'diierent ranges of measurement,v

v said indicating means including a plurality ofscales, and indiciafor indicating the leads corresponding to the ldifferent scales of said indicating means. y

19. A cable for the coil unit of an electrical measuring instrument, comprising a plurality of symmetrically located and twisted conductors permanently connected in parallel, and a plurality of other symmetrically located and twisted conductors connected in n series parallel with said first mentioned conductors.

20. A cable for the coil'unit of an electrical measuring instrument, comprising a set of conductors connected in parallel with each `othenand two sets of other conductors connected in series in each set, the two setsbeing in series parallel with the first mentioned set and the two sets beingin parallel with each other.

21. A cable for the coil unit of an electrical measuring instrument, comprising a set of conductors connected in parallel with each other, twosets of other conductors connected in series in each set, the two sets being in series parallel with the first mentioned set and the two sets being in parallel with each other, and another set of conductors in series with each other and with the said two sets. In witness whereof I hereunto subscribe mynamevthis 16 day of March, 1928.

` JOHN I-I. MILLER. 

